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Job Scheduler System Design
Visual Problem Diagram
Scenario
Midnight cron fires 50K jobs at once and your cluster oversubscribes CPUs while a payment reconciliation job waits behind a low-priority email batch. Scheduling, priority, retries, and exactly-once side effects define the interview.
Design a distributed job scheduler that runs one-off and recurring tasks across a worker pool with priorities and retries. Cron herds and non-idempotent retries cause production incidents—address both.
You should support job submit, schedule, execute, retry, cancel, and monitoring. Be ready to explain leases, priority queues, and idempotency.
Constraints
Submit job, cron schedule, priority, execute on workers, retry, cancel, status API
99.9% scheduler availability, at-least-once execution, fair multi-tenant quotas
Millions jobs/day, 10K workers, peaks at top of hour cron
Stages ahead
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